Monitoring weight gain in newborns is essential. Becoming a parent comes with one of life’s greatest responsibilities: caring for a fully dependent human being.

After birth, babies need time to adjust to life outside the womb—learning to feed, grow, and gain weight. It’s normal for newborns to lose 5–10% of their birth weight due to factors like heat loss, elimination of urine and meconium, energy expenditure, and the loss of fluid supply from the umbilical cord.

A low birth weight is a symptom, not a diagnosis, but it requires attention. This is why careful tracking of a newborn’s weight gain is so important for healthy development.

How do I know if my baby is gaining the proper weight?

After birth, a baby can lose up to 10–12% of their weight within a few days. For some, this means several grams lost quickly. Health professionals closely monitor this to ensure weight is regained promptly. Ideally, a baby should return to their birth weight within two weeks. Some will regain it quickly, even surpassing it, while others progress more gradually. This isn’t necessarily a sign of illness—each baby is unique and must be assessed individually.

On average, a healthy full-term baby gains about 30 g per day, or 210 g per week, up to three months of age. Growth then slows slightly between six months and one year. Most babies will double their birth weight by six months and triple it by their first birthday.

Your baby’s growth and development, weight gain, size and head measurements (cranial perimeter) will help health professionals monitor their growth over time. This data, taken during medical visits, is entered in your baby’s file and the curve graph developed by the World Health Organisation (WHO).

In 2010 growth curves were updated then revised in 2014 and adopted by the Canadian Pediatric Society and the Canadian Pediatric Endocrine Group (CPEG) for both babies born at term and curves for premature babies. They’re adapted based on the child’s sex, as the growth of a baby girl is different from a boy. These curves are also adapted based on different countries and population characteristics. Monitoring curves allows professionals to confirm the proper growth or quickly find nutritional or health problems in babies. But beware the tyranny of the scale!

A baby’s weight can vary depending on the scale used, as not all are perfectly calibrated. Inaccurate readings can cause unnecessary stress for both health professionals and parents. While weighing is a useful tool, the number alone shouldn’t guide decisions. A full evaluation should include observing feeding, conducting a clinical exam, assessing typical behavior, and monitoring the frequency and effectiveness of feedings.

How do you know if your baby is drinking enough?

• When he drinks, you can hear him swallow;
• He asks for his feed on his own;
• If he’s breast-fed, he sucks frequently at the breast (6 or more times a day, depending on the baby and the breast-feeding mother); if he’s bottle-fed, you can also count 6 feedings;
• He urinates 6 to 8 times a day, and is pale yellow in color;
• He has regular bowel movements (soft or pasty stools);
• He’s gaining weight.

Why do some babies gain weight more slowly than others?

Based on available statistics, 18% of newborns will struggle gaining weight after birth. Slower weight gain is caused by certain factors, both in the baby and the breastfeeding mother.

That’s why a health follow-up is needed to understand the situation and ensure appropriate support over time.

Factors that influence a baby’s weight gain

There are many factors that influence weight gain in newborns, and the following entry will explain them to you.

The factors are the following:

• Premature birth (immaturity, difficult reflex for drinking and sucking, etc.);
• A low weight baby at birth (late growth, lower level drinking, less available energy);
• Difficult breastfeeding (difficult sucking, low breastmilk flow, drowsiness, weak sucking);
• Baby’s physical conditions (short frenulum, reflux, congenital illnesses, heart problems, neurological dysfunctions, etc.)

That said, often we may not really know the causal source of slow weight gain.

Factors with a breastfeeding mother that affects weight gain

If there are no identifiable physical causes in the baby to explain slow weight gain, you need to look at issues that might deal with the mother and the delivery. Was there medication or not? Difficulty delivery? Stress? And in managing breastfeeding?

• Insufficient breastmilk production;
• Thyroid gland problems (hypothyroidism influences a lowering of breastmilk productions after birth);
• Breast insufficiency or reduction (less glandular matter to produce milk and surgery may have severed the nerve endings required to stimulate milk production);
• Loss of a lot of blood during delivery (less body liquids available for the production of milk);
• Severe diet of under 1500 calories/day;
• Delivery complications such as pre-eclampsia;
• Premature birth (increased stress in the mother and possible placenta retention);
• Use of medications or drugs that can influence milk production, such as certain oral contraceptives for example;
• We know that high and recurring stress can diminish the ejection reflex and can be the source of a milk production or slow flow problem in the mother;
• Weak or absent ejection reflex.

You should understand that a professional must first understand the basic problem surrounding the difficulty in weight gain to plan their strategy. The cause must be dealt with to improve the situation. Suggestions will be made based on the elements that are present and on which we can act, both for the mother and baby.

If slow weight gain seems to be associated with the insufficient production of breastmilk or attributable to a slow milk flow in the baby’s mouth, a series of measures can be taken to correct the situation. I have mentioned some in my entry on Insufficient or Lack of Breastmilk.

Weight Gain in a Premature Baby

Concerning weight gain in a premature baby, you need to first identify the degree of prematurity. A baby born at 37 weeks minus 1 day is identified as a premature baby. But it won’t have the same sucking capacity as a premature baby born between 30 and 36 weeks, or a very premature baby born between 23 and 30 weeks.

When breastfeeding a premature baby, it’s difficult for those born before 34 weeks to coordinate their sucking reflex with breathing and swallowing. We see babies suck in short bursts rapidly but their lips have blue contours as they’re not properly breathing at the same time. This is directly associated with the immaturity of their brain. It must adapt to the reality of life outside the uterus. Each baby will have their challenges to face. However, many times I have seen very small babies drink impressive amounts and fight to live. Just because a baby is born at 35 weeks doesn’t mean they will have problems with feeding. They have everything they need to be breastfed by their mother. All we have to do is help her with milk flow and encourage the baby to take her breast.

It’s preferable to give the mother’s milk to a baby born before term. All the virtues of breast milk will have a major impact on the premature baby’s health as this milk:

• Is easier to digest;
• Is better tolerated by the baby;
• Contains more antibodies to fight several potential infections;
• Contains essential fatty acids to help brain development and provide the baby with energy to feed;
• And much more…

On the other hand, most of the time the mother must stimulate their milk production mechanically. They will use a double electric breast pump to start the demand in her system. The pumped milk will then be used to force-feed or complete a feeding for the baby, who isn’t always able to do it themselves. It might be necessary to use supplementation, the use of a feeding tube, if breastfeeding isn’t going well despite all efforts to help the mother. But this isn’t routine.

Monitoring all aspects of a baby’s weight and growth can be challenging. Health professionals track not only weight gain, but also length and head circumference, based on each baby’s individual pace and characteristics. Understanding this aspect of newborn health can help reassure parents, as it is often a common concern.

A usefull tool : the OMS growth charts from CHU Sainte-Justine.

Marie Fortier
The Baby Expert

References :

• https://cpeg-gcep.net/fr/content/les-courbes-de-croissance-de-loms-pour-le-canada

• https://cps.ca/fr/tools-outils/courbes-de-croissance-de-loms

Updated article : March, 2025.